1. Field of the Invention
The present invention relates to a liquid crystal composition for liquid crystal display.
More particularly the present invention relates to a liquid crystal composition used for high multiplex display devices, and a liquid crystal display device that uses the same.
2. Prior Art
With the recent rapid development of information apparatuses, particularly portable terminal apparatuses, the demand for small-sized, thin and low-power comsumption display devices whose display capacity and display quality correspond to those of the conventional CRT is increasing. Liquid crystal devices meet the demand for small-sized, thin and low-power consumption display devices and have been used customarily in watches and desk-top calculators and as display terminal apparatuses whose duty is on the order of up to 1/100 by the multiplex drive of the TN-type liquid crystal cell whose twist angle is 90 degrees, and in principle it is regarded as difficult to increase the duty number because it lowers the display quality.
On the other hand, the super twist birefringence effect mode (hereinafter abbreviated to SBE mode) is suggested that uses the birefringence effect of a liquid crystal cell whose twist angle is set between 180 and 270 degrees, which is the limit where the bistability of the electrooptical properties of chiral nematic liquid crystals occurs
It is reported by T. J. Scheffer et al. {T. J. Scheffer, and J. Nehring: Appl. Phys. Lett. 45, 1021 (1984)} that this SBE mode allows the same driving method as in matrix display of the common 90-degree twist TN mode driven by the fast scan addressing mode that responds to the effective value of the applied voltage, and the SBE mode has far better contrast and wider visual angle than those of 90-degree twist TN display.
Properties required for liquid crystal compositions used in display devices of the SBE mode are the following:
(1) the voltage-transmission property is steep;
(2) the transition temperature of the nematic-isotropic phase (hereinafter abbreviated to the transparent point (clearing point));
(3) a suitable optical anisotropy value (hereinafter abbreviated to .DELTA.n) can be taken in accordance with the cell thickness (hereinafter abbreviated to d);
(4) the viscosity is low.
The property under (2) is required in the SBE mode to suppress the occurrence of hue changing of the display accompanied with the temperature dependency of the .DELTA.n, thus it is desired that the transparent point is as high as possible.
The property under (4) is particularly effective to shorten the response time in the liquid crystal cell of the SBE mode.
The assignee of the present application filed, as a prior application, Japanese Patent Application Laid-Open No. 152334/1988 (U.S. Ser. No. 07/079,997 now U.S. Pat. No. 4,778,620; EPO Application No. 87 111048.2), which is not prior art against the convention date of the present application.
The prior application discloses a tolan derivative represented by the formula: ##STR5## wherein R.sup.1 is an alkyl group or an alkyloxy group having 1 to 10 carbon atoms, R.sup.2 is an alkyl group of 1 to 10 carbon atoms, X represents --CH.sub.2 CH.sub.2 -- or a single bond, and A represents H or F, provided that when X is a single bond, A is F.